A condemned Ohio inmate appeared to gasp several times and took more than 15 minutes to die Thursday as he was executed with a combination of drugs never before tried in the U.S.

Dennis McGuire's attorney, federal public defender Allen Bohnert, called his client's death "a failed, agonizing experiment by the state of Ohio."

McGuire's attorneys had attempted to halt his execution last week, arguing the untried method put him at substantial risk of "agony and terror" while straining to catch his breath as he experienced a medical phenomenon known as air hunger.

McGuire made loud snorting noises during one of the longest executions since Ohio resumed capital punishment in 1999.

The state used intravenous doses of two drugs, the sedative midazolam and the painkiller hydromorphone, to put McGuire to death for the 1989 rape and fatal stabbing of a pregnant woman, Joy Stewart. The method was adopted after supplies of a previously used execution drug dried up because the manufacturer put it off limits for capital punishment.

Executions with the former method were typically much shorter and did not include the types of sounds McGuire uttered.

A few minutes before McGuire was put to death, state prison director Gary Mohr said he was confident the execution would be carried out in a humane and dignified manner. As is common practice, prison officials did not immediately comment after the execution except to release the time of death.

Strapped to a gurney in the execution chamber, McGuire thanked Stewart's family for their "kind words" in a letter he apparently received from them.

"I'm going to heaven, I'll see you there when you come," he said through a microphone held by the warden.

As his adult children sobbed a few feet away in a witness room, McGuire opened and shut his left hand as if waving to his daughter, son and daughter-in-law.

More than a minute later he raised himself up, looked in the direction of his family and said, "I love you. I love you" — his words audible even though the microphone had been removed.

McGuire was still for almost five minutes, then emitted a loud snort, as if snoring, and continued to make that sound over the next several minutes. He also soundlessly opened and shut his mouth several times as his stomach rose and fell.

"Oh my God," his daughter, Amber McGuire, said as she observed her father's final moments.

A coughing sound was Dennis McGuire's last apparent movement, at 10:43 a.m. He was pronounced dead 10 minutes later.

Attorneys for the state called McGuire's bid to halt his execution with the untried method an "eleventh hour" appeal based on claims that should have been raised years ago, because the process had been in place as a backup method.

Page 2 of 2 - And although the U.S. Constitution bans executions that constitute cruel and unusual punishment, that doesn't mean procedures are entirely comfortable, the state argued.

Frost sided with the state but acknowledged the new method was an experiment. At the request of McGuire's lawyers, he ordered the state to photograph and then preserve the drugs' packaging boxes and vials and the syringes used in the execution.

Bohnert, McGuire's attorney, said the court's concerns over the method had been confirmed.

"And more importantly, the people of the state of Ohio should be appalled at what was done here today in their names," said Bohnert, who did not witness the execution.

McGuire, 53, was executed for killing Stewart, a newlywed who was eight months pregnant at the time of her death, in western Ohio's Preble County.

"We have forgiven him, but that does not negate the need for him to pay for his actions," said a statement released by Carol Avery, Stewart's sister, after McGuire's death.

Stewart's slaying went unsolved for 10 months until McGuire, jailed on an unrelated assault and hoping to improve his legal situation, told investigators he had information about the woman's Feb. 12, 1989, death. His attempts to blame the crime on his brother-in-law quickly unraveled and soon he was accused of being Stewart's killer, according to prosecutors.

More than a decade later, DNA evidence confirmed McGuire's guilt, and he acknowledged that he was responsible in a letter to Gov. John Kasich last month.

"One can scarcely conceive of a sequence of crimes more shocking to the conscience or to moral sensibilities than the senseless kidnapping and rape of a young, pregnant woman followed by her murder," Preble County prosecutors said in a filing with the state parole board last month.

His attorneys argued McGuire was mentally, physically and sexually abused as a child and has impaired brain function that made him prone to act impulsively.

"Dennis was at risk from the moment he was born," the lawyers told the parole board. "The lack of proper nutrition, chaotic home environment, abuse, lack of positive supervision and lack of positive role models all affected Dennis' brain development."

Documents obtained by The Associated Press show McGuire unsuccessfully sought a reprieve in recent weeks to try to become an organ donor. In November, Kasich granted a death row inmate an eight-month reprieve to let the prison system study his request to donate a kidney to his sister and his heart to his mother.

Kasich said McGuire couldn't identify a family member who would receive his organs, as required under prison policy.